Heparin, antithrombin III and the like are currently used as anticoagulants. With regard to thrombolytic agents, urokinase isolated from urine or cultured kidney cells, streptokinase isolated from .beta.-hemolytic streptococcus and the like have been put into practical use, as well as a recently developed tissue plasminogen activator.
These substances, however, have side effects such as bleeding tendency and show only one activity, anticoagulant activity or thrombolytic activity.
Recently, in the field of fundamental studies, a substance having an effect to inhibit blood coagulation and an effect to enhance formation of activated protein C which enhances fibrinolysis has been found in a rabbit lung tissue extract by N. L. Esmon et al. and named thrombomodulin (J. Biol. Chem., Vol. 257, p. 859, 1982). It has been reported by Maruyama et al. that thrombomodulin is a thrombin receptor localized on blood vessel endothelial cells and that thrombin is deprived of its blood coagulation activity when bonded to thrombomodulin and the thrombin-thrombomodulin complex activates protein C to impart its anticoagulation effect (J. Clin. Invest., Vol. 75, p. 987, 1985). In other words, it is possible that thrombomodulin imparts effects of both inhibiting blood coagulation and enhancing fibrinolysis and therefore can be applied to clinical means.
The following summarizes examples on the isolation of human thrombomodulin so far reported. In this instance, unless otherwise noted, data on the molecular weight cited below are those measured under non-reducing conditions by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
P. W. Majerus et al. have purified thrombomodulin from human placenta and reported its a molecular weight as 75K (J. Biol. Chem., Vol. 259, p. 12246, 1984), while Aoki et al. have purified thrombomodulin from human placenta and reported its molecular weight as 71K (Thrombosis Res., Vol. 37, p. 353, 1985; and Japanese Patent Application Kokai No. 60-199819). Maruyama et al. have purified thrombomodulin from human lung and reported that its properties were the same as those of placenta origin (J. Clin. Invest., Vol. 75, p. 987, 1985). In addition, Suzuki et al. have partially purified thrombomodulin from human platelet and determined its molecular weight as 78K and reported that the thrombomodulin preparations obtained from platelet, placenta and lung blood vessel endothelial cells had the same properties in terms of their electrophoretic behavior and affinities for thrombin and protein C (J. Biochem., Vol. 104, p. 628, 1988).
In addition to these thrombomodulin molecules purified from human organs (to be referred to as "human thrombomodulin" hereinafter), the following substances having similar properties (to be referred to as "human thrombomodulin-like substance" hereinafter) have been reported.
P. W. Majerus et al. have partially purified two human thrombomodulin-like substances from a human plasma having molecular weights of 63K and 54K, respectively, and reported that similar substances existed also in urine (J. Clin. Invest., Vol. 75, p. 2178, 1985). In addition, Ishii et al. have reported that similar substances having molecular weights of 105K, 63K, 60K, 33K, 31K and 28K (no description about reducing or non-reducing measuring condition) were excreted into urine (Abstracts of Papers, the 108th Meeting of Pharmaceutical Society of Japan, 6F05, 11-1, 1988). Other examples of human thrombomodulin-like substances obtained from urine include a mixture of substances having molecular weight of 200K, 48K and 40K (Japanese Patent Application Kokai No. 63-30423) and those having molecular weight of 39K and 31K (Japanese Patent Application Kokai No. 63-146898).
C. T. Esmon et al. have prepared a chemically synthesized peptide which corresponds to a portion of the thrombomodulin molecule (Japanese Patent Application Kokai No. 2-19399).
On the other hand, Suzuki et al. have cloned a gene of human thrombomodulin precursor containing a signal peptide from a human lung cDNA library making use of genetic,engineering techniques, determined entire structure of the gene and revealed an amino acid sequence of 557 amino acid residues with a signal peptide of 18 amino acids adjacent to the sequence, with a conclusion that the N terminal amino acid sequence of human thrombomodulin was Ala Pro Ala Glu Pro (EMBO Journal, Vol. 6, p. 1891, 1987). In addition, Suzuki et al. have reported that activity of the human thrombomodulin prepared by genetic engineering techniques was the same as that of natural human thrombomodulin purified from biological tissues (J. Biol. Chem., Vol. 264, p. 4872, 1989) and that the human thrombomodulin-like activity was restricted to a portion of the amino acid sequence, from 345 position to 462 position amino acid residues numbered from its amino terminus, and the activity disappeared when any amino acid in the active portion was deleted (J. Biol. Chem., Vol. 264, p. 10351, 1989; and Abstracts of Papers, the 12th Meeting of International Society of Thrombosis and Hemostasis, p.334, Title No. 1039, 1989). Also, R. W. Jackman et al. have determined complete structure of a gene of human thrombomodulin precursor and revealed an amino acid sequence of 559 amino acid residues with a signal peptide of 16 amino acids adjacent to the sequence, with a conclusion that the N terminal amino acid sequence of human thrombomodulin was Phe Pro Ala Pro Ala Glu Pro (Proc. Natl. Acad. Sci. USA, Vol. 84, p. 6425, 1987). Also, D. Wen et al. have cloned a gene of thrombomodulin precursor from a human umbilical cord vein cDNA library, determined complete structure of the gene and revealed an amino acid sequence of 554 amino acid residues with a signal peptide of 21 amino acids adjacent to the sequence, with a conclusion that the N terminal amino acid sequence of human thrombomodulin was Glu Pro (Biochemistry, Vol. 26, p. 4350, 1987).
Also, Andersen et al. have attempted to produce a human thrombomodulin-like substance which corresponds to a moiety of the human thrombomodulin molecule, by means of genetic engineering techniques (International Patent Application WO 88/09811).
In addition, P. W. Majerus et al. have developed a cDNA clone of human thrombomodulin by means of genetic engineering techniques and succeeded in expressing a protein molecule having complete amino acid sequence of human thrombomodulin (Japanese Patent Application Kokai No. 63-301791).